of berlin



' eaoaen a.

Patented 8, 1932 iU-NlTEDlSTA TES PATENT OFFICE CHEMICAL PULPING rnocnss No Drawing.

This invention relates to a chemical pulping processin which two different types of chemical liquors are employed in succession in order to liberate pulp from the raw cellulosic material. It has for its aim the production of high grade cellulose pulps, not only from the usual woods, such as spruce, used for the production of sulphite pulps so called, but also from woods of high resin content.

In accordance with the process of the present invention, the raw cellulosic material is initially cooked short of fiber liberation in a solution of sodium sulphite, whereupon the cooked material is then cooked to complete fiber liberation in a sulphurous acid solution containing bisulphites, if desired- Such a two-step process is particularly advantageous when applied to resinous or gum-containing wood, such, for example, as ,birch, for the reasonjthat the initial cook results in the removal from the wood, .not only of ligneous matter, but of considerable resin, which constituent is quite resistant to the action of acid woods as a raw material in the process of the present invention, on the other hand, results in a pulp which is of distinctly lower resin content and which, therefore, may be bleached more readily and may be formed into paper without impairing the papermaking machine. '9

Various examples: of procedure falling within the purvyew of the present invention I, order to produce the pulp are ossible. Accordingly, I shall cite here-. ina ter a variety of conditions under which the two cooking steps ma be carried out in esired from woods, such as spruce, fir, birch, etc. When the initial cookingliquor consists of a solution of Application filed June 12,

monrnn, or BERLIN, raw HAMPSHIRE, ASSIGNOR 'ro BROWN county,

or BERLIN, NEW nmrsnmn, a CORPORATION or MAINE 1980. Serial No, 460,793.

only sodium monosulphite, the two cooking operations may advantageously be carried out in a single digester, which is lined to resist the acidity of the second cooking liquor.

.Such a procedure carries with it a further advantage when a wood of comparatively low resin content, such as spruce, is employed as a raw material,- as 1n such case, after the 1mtial cooking'operation has been completed,

sulphurous acid, preferably in liquid form or in the form of a concentrated solution, may be added to the liquor to form a bisulphite solution in which cooking to complete fiber liberation may be effected. It is, however,

undesirable to form the second cooking liqnor from the residual liquor of the first cooking operation when the wood being processed is ofhigh resin content, as'the conversion of the residual liquor to an acid condition would be accompanied by the precipitation of considerable resin, which would be adsorbed on the resulting pulp. The initial cooking liqnor may consist of a solution of sodium sulphite of 1% to 5% strength, and cooking of the wood therein in the form of chips may be effected under atmospheric or superatmospheric pressure conditions. For example, cooking may be effected in a closed digester for three to five hours, in a 2% solution of sodiumsulphite at from 250 to 335 F., at the end of which time the chips are intact, even though extraction of resins, siliceous -matter, and other components has been effected therefrom. The elimination of resins and siliceous matter from the wood may be promoted by adding a small amount of alkali to the liquor, say, 1% to 2% of caustic soda or sodium sulphide, or 0.2% to 0.4% of sodium carbonate or sodium phosphate. These alkalies are of advantage in saponifying or in emulsifying the resins present in the wood, but they needCnot be used when the woods are not particularly high in resins, as is the case with spruce; and when they are used, they should not be present in amounts in excess of those hereinbefore given, as the presence of excessive alkali in the initial cooking liquor seriously retards fiber liberation in the second cooking liquor.

After the initial cooking operation, the

chips are washed either thoroughly or incompletely, depending upon the type of wood used as a raw material. Thus, when a resinrich wood is employed, it is preferable that the cookedchips be washed as thoroughly as possible, in order to remove the resin reaction products, including resin soap, which isprecipitated by' the action of the acid liquor employed in the second cooking operation. But

the use of spruce or other wood of low resin content does not call for complete washing; and, in fact; it may be desirable to leave hehind in the chips sodium sulphite, to permit forming more or. less bisulphite when a sul hurous acid solution is added to the chips. he formation of bisulphite with residual sulphite in the chips makes possible the production, of a high grade uniform pulp, as

such residual sulphite is distributed uniformly throughout the chips and the sulphurous acid immediately penetrates the chips to form bisulphite, which checks hydrolyzlng action on the fiber by the sulphurous acid. It is, however, posslble to realize high yields of good quality pulp, even when the sulphurous acid solution used in the second cooking operation does not contain bisulphite either added,

thereto or formed from residual sulphite present in the chips. All the sodium" constituent is thus used in a neutral or alkaline liquor, so that in recovering the valuable sodium constituent from the spent liquor by suitable recovery operations, acid-proof apparatus isunnecessary; and the spent liquor resulting from the cooking operation may be discarded. The conditions under which the second cooking operation is eifected depend, among other factors, not only upon the composition of the second cooking liquor, but also upon the conditions employed during the initial cooking operation. Consequently, I

shall now give a specific example of procedure involving definite conditions from the beginning to the end of the process. Spruce chips, such as customarily used in making. chemicalwood pulps, were placed in a pulp digestervalong with a 5% solutionofsodium sulphite, and the digester was closed. The digester charge was heated to 300 F. in an .hour and was maintained at this temperature for three hours. The digester contents were then vremoved and the cooked chips, were washed thoroughly to remove sulphites. The washed chipswere then digested in a 5% sulphurous acid solution, which washeated to 260 F. in two hours and then maintained thereat .for two more hours, with the pressure not in excess of 75 pounds. At the end of this cooking operation, a long-fibered pulp was obtained in the amount of 52%, based on.

the wei ht of the dry wood used as a raw materia which amount is somewhat in excess of the usual pulp yields realized in the acid sulphite process of fiber liberation. The

product possesses characteristics analogous to those associated with a high grade sulphite pulp, in that it is easily bleachable and possesses relatively high strength and better than tolerable tear resistance. 7

It is to be noted that neither of the cooking operations just described is capable of liberating pulp from the raw wood when practised alone. Thus, one does not derive pulp from the raw spruce wood, even when it is cooked as long as ten to fifteen hours in a 5% sodium sulphite solution at temperatures of 300 F. Again, a solution of sulphurous acid alone is incapable of converting raw wood into a satisfactory pulp under any conditions of treatment of which I am aware. When used after the wood has been cooked in a solution of a sulphite; it completes the fiber liberation initiated by the sulserviceable for those uses to which sulphite pulp is put. If the entire process is to be carried out in a single digester, the initial cooking liquor may be of lower sodium sulphite concentration, since residual sodium sulphite present in the spent liquor from the initial cooking operation serves to promote fiber liberation after such spent liquor is treated with sulphurous acid to form the second cooking liquor, in which cooking is continued. Thus, the raw wood in the form of chips may be'cooked for four hours in, say,

a 2% solution of sodium sulphite at a temperature of 300 F.', whereupon thecharge of cooked chips and solution may be allowed to cool to a temperature of, say, 275 to 280 F., at which tem erature suflicient sulphurous acid either 'as a iquid or as a very strong solution may be added thereto in amount sufiicient to form a solution containing, say, 5%

to 7% free S0 The cooking operation may phite solution to produce a high grade pulp then be continued in the resulting sulphuronlysulphite mentioned because of its comparatively high solubility, et sulphites of the other alkali metals or of t e alkaline earth metals, such as magnesium,

present invention.-

I claim: 1. A process which comprises cooking chipped wood short of pulping in a non-acid solution of a sulphite, and then cooking'in a solution of sulphurous acid to complete fiber liberation.

2. A process which comprises cooking may be employed without departing from the principles of the chipped woof short of pullpi' mg in a non-acid solution of sodlum sulp to, washing the cooked material, and then cooking in a solution of sulphurous acid to complete fiber liberation.

3. A process which comprises cooking chi ped wood short of pulpin in a nonacid solution of a sulphite, and t en cooking in a sulphurous acid solution of a sulphite to complete fiber liberation.

4. A process which comprises cooking wood chips short of pulping in a non-acid solution of sodium sulphite, washing the cooked chips incompletely free of sodium sulphite, and then cooking the chips in a solution of sulphurous acid'to complete fiber libera tion.

5. A process which comprises cooking wood chips short of pulping in a. non-aci solution of sodium sulphite, adding sulphurous acid to the solution to convert it into a sulphurous acid solution of a sulphite, and continuing cooking in the solution to complete fiber liberation.

6. A process which comprises cooking wood chips of a resinous character short of pulping in a somewhat alkaline solution of sodium sulphite, washing the cooked chips and then cooking the chips in a solution 0 sulphurous acid to complete fiber liberation.

In testimony whereof I have afiixed my signature.

GEORGE A. RICHTER. 

